Migrating from 32bit to 64bit Linux

About

I ran lots of different systems:

• NetBSD (on digital alpha, on 68K Macintosh and PPC Macintosh)
• PowerPC Linux (on PowerMac G3)
• Debian (VM) for the last 15 years or so, hosted with my favourite hoster, Mathias Peter.

How we made it

ℹ️	This will also apply if you just move to another hardware or VM.

About the approach

In theory, you can exchange the i386 by with amd64 binaries. We tried that, failed several times, and finally gave up. The approach shown here is (in our opinion) the most viable option.

The basic idea

• Install a new system, matching your distribution release, in this case debian 11.6
• Install the same packages, but in 64bit
• Move /etc and /var to the new system
• Stop the old system
• Mount /home on your new system
• Reboot

In detail

• Make backups and snapshots
• Make sure all packages are installed, f.e. like this

# Do this on the old system
dpkg -l |grep '^ii' |awk '{print $2}' |sort > dpkg_list_oldserver.txt

# Do this on the new system
dpkg -l |grep '^ii' |awk '{print $2}' |sort > dpkg_list_newserver.txt

# Compare installed and install missing packages
diff dpkg_list_oldserver.txt dpkg_list_newserver.txt |grep '^<' |awk '{print $2}'
diff dpkg_list_oldserver.txt dpkg_list_newserver.txt |grep '^>' |awk '{print $2}'

• Disable /etc/cron.d/certbot
• Make sure, all mods are installed: ls -1 /etc/apache2/mods-available
• Copy the needed portions of /root to your new machine
• Put Nextcloud in maintenance mode: sudo -u www-data php occ maintenance:mode --on and wait 5 minutes
• Stop services on old system

apachectl -k stop
/etc/rc6.d/K02dovecot stop
/etc/rc6.d/K01postfix stop

• Set your Mediawiki to $wgReadOnly
• Just in case, dump the databases

mysqldump -u root -p --databases MEDIAWIKI_DB > mediawiki_2023-04-03.sql
mysqldump -u root -p --databases NEXTCLOUD_DB > nextcloud_2023-04-04.sql

• First /etc, then /var!
• For moving /etc do this on your new system:

cd /
mv /etc /etc_old
ssh root@OLDSYSTEM "cd /; tar cf - etc" |tar xvf -
cp -pr /etc_old/fstab /etc/

• For moving /var do this on your new system:

cd /
mv /var /var_old
ssh root@OLDSYSTEM "cd /; tar cf - var" |tar xvf -
rm -r /var/cache/apt /var/lib/apt /var/lib/aptitude /var/lib/dpkg
cp -pr /var_old/cache/apt /var/cache/
cp -pr /var_old/lib/apt /var/lib/
cp -pr /var_old/lib/aptitude /var/lib/
cp -pr /var_old/lib/dpkg /var/lib/

• Shutdown old system and mount /home on new system
• Reboot new system
• End maintenance mode: sudo -u www-data php occ maintenance:mode --off
• Check syslog and daemon.log
• Check /var permissions
• Test all services
• Test aptitude/dpkg:

apt list --installed
dpkg -l
apt-get update
apt-get dist-upgrade

✅	That's it!

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Footnotes: